For a repository is large and had many activities (such as creating branches, creating tags, pushing commits, commenting on issues), after first adding it, only recent pull requests are synchronized and show up on the pull request details dialog on the view issue page. Older pull requests after certain time never show up.

This also happens when you have such a large repository added for a while, and does a full synchronization.

The cause of the problem is that the DVCS Connector uses the GitHub repository events api to pull down historical events about pull requests. But this api has a limit of only returning up to 300 events at most. This would limit the synchronization to retrieving at most up to 300 pull requests, assuming all events are about pull requests. In practice, this number is much lower as not all events are for pull requests and even for those that are, not all of them are for pull request creation.

Just as an example, on one repository, only 60 out of 300 events are for pull requests:

 117     "type": "PushEvent",
  80     "type": "IssueCommentEvent",
  60     "type": "PullRequestEvent",
  24     "type": "CreateEvent",
  19     "type": "DeleteEvent",

And only 30 out of the 60 pull request events are for opening a new pull request.